1. Field of the Disclosure
This disclosure relates to a method for removing soot from exhaust gases. In particular, this disclosure relates to a method for oxidizing soot from diesel exhaust gas from a diesel engine, a diesel exhaust gas treatment system, a method of providing a catalyst composition on a diesel particulate filter, and a catalyst composition for facilitating soot oxidation. The catalyst composition is a doped or undoped manganese oxide octahedral molecular sieve (OMS-2) material (e.g., cobalt doped manganese oxide octahedral molecular sieve (OMS-2) material).
2. Discussion of the Background Art
In general, diesel engines are advantageous because they have various uses due to their high power and ability to be operated even under high loads. However, since exhaust gases discharged from such diesel engines are a major source of air pollution, their allowable discharge standard becomes more and more strict throughout the world. The main pollutants from diesel engines include fine soot particulates, hydrocarbons, carbon monoxide, soluble organic solvents, and nitrogen oxides. In particular, the soot particulates directly impact life, such as increasing a generation rate of cancer of the respiratory organs.
In recent years, environmental regulations in the United States and Europe restricting diesel particulate emissions have necessitated improvements in the removal of particulates from diesel engine emissions. Such particulates generally consist of carbonaceous particulates in the form of soot.
At present, there are two major diesel particular filter (DPF) regeneration techniques; active regeneration and passive regeneration. In active DPF regeneration the particulate matter is periodically oxidized either using a heater/a flame based burner at elevated temperatures (above 600° C.) or by increasing the exhaust gas temperature. This flame based technique possesses serious fire hazard and also due to the elevated temperature, the filter matrix could breakdown and cause damage to the internal engine parts. Another drawback of this method is the poor regeneration efficiency, resulting in deposition of up to 35% of soot on the filter. This method also consumes a large amount of energy during the heating process thereby decreasing the fuel efficiency of the engine.
In passive regeneration, the particulate matter is oxidized by means of an on-going catalytic oxidation process. The method is both economically and environmentally preferred since it requires no additional energy source, occurs at exhaust gas temperature, very simple, effective, and fuel efficient. However, finding a catalyst which is capable of decreasing the soot combustion temperature from 600° C. to diesel engine exhaust temperature (typically 150-400° C.) and also carryout complete oxidation of soot to CO2 without toxic CO gas is challenging.
In most cases, the filter is coated with precious metals including platinum group metals (PGM) such as Pt and Pd. However, these metals are very expensive and they also highly active in undesirable reactions such as oxidation of SO2 to SO3. In addition to PGM, Ag with an active metal (Cu, La, Co, Ni, Mn, Fe, Ce) oxide component has also been used in DPF coatings. However, these materials are capable of oxidizing soot at temperatures between 500-600° C., which are much higher than the diesel engine exhaust temperatures. Therefore, additional energy is required to drive the oxidation.
Furthermore, currently most of the catalysts generate a considerable amount of CO during the combustion of diesel soot which, is a byproduct from incomplete oxidation and possesses serious health hazard. In addition, most of the currently used catalysts require a high catalyst to soot ratio which reduces its efficiency in the real applications. Thus, it is desirable to develop a diesel soot oxidation catalyst which is highly active at diesel engine exhaust temperatures, highly selective towards CO2, much greener, highly efficient, and less expensive.
The present disclosure provides many advantages over the prior art, which shall become apparent as described below.